388 CHORD ATA. 



In comparing this arrangement with that of the pigeon, we 

 notice the absence of renal portals and a different relation- 

 ship of the posterior veins caused by the backward extension 

 of the kidneys in the latter. Hence there is nothing in the 

 rabbit approaching the ''renal cycle" of the pigeon. 



The arterial system has two parts. The pulmonary 

 system consists of a pair of large but short pulmonary 

 arteries leading from the right ventricle to the lungs. The 

 left pulmonary artery is connected with the dorsal aorta by 

 a transverse vessel, the ductus arteriosus. (Plate XIII.) 

 It is only functional in the embryo, becoming a solid band 

 in the adult. 



The systemic system consists of two main arteries which 

 separate soon after emergence from the left ventricle. The 

 right innominate runs forwards and outwards, and divides 

 into the right carotid to the head and right subclavian to 

 the fore-limb and shoulder. The aorta bends forwards and 

 outwards to the left, and gives off a left carotid to the head, 

 then a left subclavian^ and is continued backwards to the 

 left of the mid-dorsal line through the diaphragm which 

 it supplies by a small phrenic artery breaking up on the 

 surface of the diaphragm. It lies dorsal to the postcaval 

 to the hind-end of the body where it' comes round and lies 

 ventral to it. It gives off a median unpaired coeliac to liver, 

 stomach and spleen, anterior mesenteric to the intestine and 

 pancreas dind posterior mesenteric to the rectum, paired renals 

 and genitals to kidneys and genital organs, and then divides 

 into two common iliacs which give off ilio-lumbars and in 

 turn bifurcate into femoral and internal iliac. The persist- 

 ence of the left aortic arch alone instead of the right, as in 

 the pigeon, should be noted. Again, there is only one 

 (right) innominate artery, the left carotid and subclavian 

 communicating directly with the dorsal aorta instead of 

 forming a separate left innominate, as in the pigeon. It 

 will be remembered that in the frog the subclavians (or 

 brachials) come off from the aortic arch on each side, so 

 that the rabbit must be regarded as the more primitive in 

 having only one innominate. However, the arrangement 

 of carotids and subclavians varies very much throughout 

 the Mammalia. Lastly, the very close correspondence 

 of the arterial and venous system is striking. With the 



